Planetary rovers

Planetary Rovers Might Roam Better

with an Elastic Loop Mobility System

April 28, 1998: Reviving a 65-year-old English invention might give planetary explorers a better footing on other planets, and a better view as they roll along.

Odd though it may seem, only six planetary craft have actually been driven around on other worlds. U.S. astronauts drove three Lunar Rover Vehicles on the last three Apollo missions, and the former USSR landed two automated Lunokhod rovers that moved around under remote control. Finally, in 1997, the United States placed the first rover, Sojourner, on the surface of Mars.

Dr. Nicholas Costes, a senior research scientist at NASA's Marshall Space Flight Center, and Dr. Stein Sture of the University of Colorado believe that dusting off an old design will improve mobility for planetary craft as mankind dispatches more rovers to Mars. (Costes and Sture are project scientist and principal investigator, respectively, on the Mechanics of Granular Materials experiments aboard the Space Shuttle.)

The design predates the Space Age by a quarter century, and at one point might have gone to the moon. It's the Elastic Loop Mobility System (ELMS), part tank tread, part wheel, and highly promising.

of the Elastic Loop Mobility System and a model of a mobile Viking lander.

The original idea came from a 1933 patent by J.G.K. Kitchens for an "endless traveler track band." Kitchens, an Englishman, proposed using a continuous, elastic track to move vehicles through loose soil and mud. The track would curl across its width so the section between wheels would flatten out and hold the track taut. Tanks and bulldozers, by comparison, have treads made of multiple, interlocked shoes.

The problem with the original design was it used two large wheels at front and back. These tended to jam rocks between the track and the wheels, so it never progressed beyond test models, despite the great promise of eliminating several moving parts.

For the Lunar Rover Vehicles on Project Apollo, NASA developed a wire mesh wheel that would not go flat. Working on improved designs, Costes revived Kitchens' idea with an interesting variation.

A model of a rover, with three elastic loops, just after deployment on a planet surface. Links to

The variation developed by Costes (working in cooperation with the late W. Trautwein, then of Lockheed Missiles & Space Co.) raised the main wheels, added a load wheel next to each main wheel, and used modern materials to make a stiffer, more robust track. This turned the track into a spring that elevated the vehicle and let rocks and dirt fall off before they could jam the main wheels.

The new design also spread the vehicle's load over a larger area, giving the vehicle better traction in a smaller package than it could get with wheels.

The drawing at right depicts the basic design of the ELMS. A working vehicle could be much longer with little change in this outline. Links to

Tests on simulated lunar soil at the U.S. Army's Waterways Experiment Station showed that the loop wheel, as they sometimes called it, performed better than the Lunar Rover wheels. Loop wheel vehicles could climb 35-degree slopes, compared to an 18-degree maximum for the Lunar Rover, and could climb obstacles twice as large as those of conventional treaded vehicles. The quality of the ride was improved, too.

The Apollo program ended before the ELMS could be applied to later rovers. In 1972, Martin Marietta, the prime contractor for the Viking Mars landers, rediscovered the ELMS. At the urging of the director of NASA's Langley Research Center (which managed Viking), Costes started developing concepts so a Viking Mars lander could roam. The first two Mars landers were already in development, but managers at Langley hoped that a proposed Viking '79 (right) might be fitted to move. That was never funded, either.

A model of a proposed Viking 3 lander is outfitted with ELMS for demonstration tests. (top links to

), with metal wheels, readied for flight), NASA is preparing to launch a new generation of planetary craft, and Costes and Sture are proposing that the ELMS concept get another look for planetary missions.

"Because of the proven superiority in its performance characteristics," Costes said, "the ELMS appears to offer substantial advantages for future Martian and other planetary exploration."

The value goes beyond a smooth ride and the ability to climb steep hills. An ELMS rover would also be sure-footed, providing a stable platform for science equipment to pick up samples or to drill core samples.A stable platform will be especially important, Costes contends, because the rover and its excavation equipment will have to be lightweight to reduce costs.

It would also give science instruments on a rover a better view of the terrain since the tracks would be closer to the ground than instruments on other rovers.

. The others were scanned from a 1973 paper by Costes and Trautwein. The images range from 1391x877 to 1516x815 pixels and 627K to 517K in size. Because they were scanned from a halftone copy, the quality is low and some manipulation may be required.